Aluminum alloy



Patented Aug. 7, 1,945

as smor Ira M. Le Baron, Arnold, pa, mm, to Aluminum Company of America,Pittsburgh, Pa, a corporation of Pennsylvania No Drawhlg. Application@ctobcr H2, 2042,

Serial No. 181,721

(oi. ssss) 6 Claims. This invention relates to aluminum base alloys andmore particularly to aluminum base alloys containing substantial amountsof copper and small amounts of other specific alloying elements forimproving the tensile properties oi the alloy in'the heattreated andprecipitation hardened condition.

Aluminum-copper alloys, particularly those laluminum base alloyscontaining between 1 and 12 per cent copper. have found fiideapplication in industry and have been used in large quantiare, however,certain uses for which these alloys are employed, which requireexceptionally high tensile properties together with good resistanceties. Although these alloys in either the as-cast per alloy refers to analuminum alloy containing copper as thepredominant added alloyingelement. The terms heat treatment and solution heat treatment as usedherein signi y a treatment wherein an alloy is heated to a temperaturebelow the fusion point of the lowestmeltlng eutectic of the alloy .for atime sumcicntly long to dissolve a substantial portion of the solublealloying constituents. Artificial aging is a treatment given toprecipitation hardeningalloys, wherein the alloy' is heated to atemperature somewhat above room temperature but below the heat treatingtemperature to precipitate the alloying ingredients present in thealuminum in a supersaturated condition, a condition produced tocorrosion and good working and machining characteristics. Furthermore,these high. properties whether in the cast or'wrought alloy must remainrelatively stable over long periods of time under all operatingconditions. A notable example of the uses requiring alloys having theforegoing properties is found in the fabrication of dustry are generallyeasily met and the properties remain within relatively narrow limitsindefl-' nitely so that good performance of these light alloys'isobtained; however, constant effort is being madeto improve them in orderthat the current minimum requirements will be greatly exby rapidlycooling the alloy from the solutionheat treating temperature. The termtensile properties includes tensile and yield strength,elongationandoithealloy. The present invention is predicated on thediscovery that the tensile properties and resistance to corrosion of.solution heat treated and arti-. flcially magnesium l'ree aluminum basealloys containing copper are greatlyimproved by the addition to thosealloys of about 0.01 to 2.0 per cent of llthiumandat least one ofthe'ele-- ments selected from-the group, which for conveniencemay becalled thocadmium group. con-' sisting of cadmium, mercury, silver, tin.indium and zinc, these elements being present in the proportion of about0.01 to 1.5 per cent each of cadmium, mercury, silver, tin, indium, andabout 0.01 to 0.5 per cent of zinc, the total of these elements notexceeding about 1.6 per cent. The combination of lithium and one or moreof the elements "from the above group in the aluminum-copper It is anobject of the present invention. to p o- 4 vide a heat treatablealuminum base alloycontaining appreciable amounts of copper, havinghigh'tensile properties'and good resistance to properties by heattreating and aging. 'Still an other object of my invention is to providealuminum base alloys containing appreciable amounts of copper, whichpossess good working and machining characteristics together with highten silo properties and good resistance to corrosion.

The term aluminum base alloy as used throughaluminum by weight. The termaluminum-copcorrosion. Another object of the present invenalloys has thesurprising eifect of improving the tensile properties and resistance tocorrosion to.

. an extent much greater than the aggregatlve,

eflect of the same elements present separately in'the alloys. Lithium isnot known to have any pronounced beneficial eiiect on the tensileproperties or the alloy when not in combination with the elements'oi'this group and it is sometimes i even detrimental to the tensileproperties; how-' ever, lithium with one or more elements from thecadmium group forms a combination which exerts an unexpected andprofound influence on the properties of aluminum-copper alloys. andfurthermore,-to achieve the obiects of the present invention lithiummust be present in all combinaout the specification and appended claimsrefers to an alloy containing at least '10 per centmetallic tions ofelements from the foregoing group. lithium should be present in thealloy in amounts not less than 0.01 per cent to consistently obtain anysubstantial lint in properties, and

easilyhandledduringproductionofthealloyand. it does not have anyparticular detrimental ef- 2 V I assure group. Bilver, however, which isfounr? adjacent thisgroup ischaractericed by many-of thepropertiescommcn tothemetalsofthisgroup. From the eifect displayed bythe elements of the cadmium group on the aluminum-copper alloys and fromthe disclosurein Doanand Mahla,theseelements must necessarily beconsidered as a group.

' Lithium which flils in the "light metals Mfectsonthealloyifthemaxlmumlimit'iseb' ceeded.Cadmiummaybepresentinthealloy in amounis from 0.01 to 1.5 per centbut-the most pronounced increase in tensile properties'occurswhenitlspresentin amcimtsbetween0mand0.5percent,andaboveaboutl.5percentthereispracticallyncincreaseinpmerfl thegroupususllyhavethegreatestinnu: onthetensile' properties. 'l'he.lithium-cad-- combinationis the only exception to Whenmorethan'onemetalfromthegroup The elementsof the group which form Moll! with lithiumandim I 4 I. provepropertiesof aluminum-copper alloys are also a natural in which areelements g a number of similar chemical and physical properties, as

for example, densiiy'melting point, strength andamnity for omen. isshown in the periodic 0." Here all the metals in my group. exceptsilver. are mm in the flow melting hea y'metals" [of this periodicsystem is definitely diiierent in many of its physical and chemicalproperties from ,the elements in the low melting heavy metalsgroup, andtherefore cannot be considered in the class with the elements in'thatgroup."

The alloysto which the addition of lithium and one or more of theelements of the aforementioned group is particularly beneficial arethose containing 1 to 12 per centicopper, not

more than 1 per cent each of silicon and iron present as lm ties, andwith or without a'total of 0.01 to 1.5 cent of one or more of thehardening elementsmanganesechromium, titanium, molybdenum, tungsten,vanadium, nickel, cobalt, beryllium and boron within thefollowing'proportions for each of said elements: manganese, 0.05 to 1.5per cent: chromium, 0.05

1 per cent; titanium, 0.03 to 0.5 per cent; molybdenum, 0.05 to 1 percent; tungsten, 0.05 to 1 per cent; vanadium, 0.01 to 1 per cent;zirconium,

0.05to 0.5 per cent; nickel 0.05 to 1 per cent; cobalt, 0.05 to l percent; beryllium, 0.01 to 0.5 per cent; and boron, 0.01 to 0.5 per cent.The foregoing hardeningelements constitute a group of substances all butthe last two ofwwhich are in the "high. melting heavy metals" group ofthe table in the book by Dean and Mahlapreviously,

referred to, and which. for the purposesof my invention, are alikeinrespecttotheirhardening f effect upon the alloys of aluminumcopper-lithium and one or more metals from the cadmium group. Althoughberyllium and boron arefnot found in the high melting heavy metals groupof this-table, they have high melting points together witha number ofcharacteristics similar to the metalsin the high melting heavy metalsgroup. All the above named elementsserveto enhance particular properties-oi the alloy without substantially altering its fundamentalcharacteris- -,tics. 'lhe'pieferredrangeforcopperinthesealloys isbetween8 and 5 per cent.

The term magnesium-free alloys as herein employed refers to those alloyswhich have less than 0.01 per cent magnesium present as animpurity.Since magnesium has a definite detrimental eifecton thetensileproperties of my allow. it is desirablein commercial practice to keepthis-impurity below a maximum of 0.00.5

per cent. g

.lhe solution and aging treatments for alumihum-copper 'alloyscontaining lithium and one or more metals from the cadmium group arenotmaterially different from the convenflonal treatments given toaluminum-copper alloys, i. e., a solution treatment wherein the alloy isheated to a temperature suillcientiy highand for a period of timesuillciently long to dissolve the soluble constituents. This heattreatment is conventionally carried out for aluminum-copper alloys at abetween 550-1000 I". for a period of timehetween 15 minutes and 8 home.The alloy isthenquenched'andsrtiflcialiy'aged. In the aging treatmaitthe quenched alloy is'held at a temperature between250and400' l'.for4to20 hours. No special conditions or equipment are requiredto heat treatand age myali ya The lmprovementinaluminum-copper alloys addition oflithium and one or more metals from the cadmium group occurs in eitherthe cast or wrought alloys and in addition to the high tensileproperties and resistance to corrosion, these alloys possess goodmachining and workingc'haracteristics. v

The effect of the combination of lithium and an element selected fromthe cadmium group on the tensile properties of aluminum-copper alloysmay be illustrated from the following observations. An aluminum basealloy nominally containing 4.5 per cent copper, 0.8 per cent manganese,0.25 per cent silicon and 0.15 per cent iron was melted and divided intothree portions, one

portion being used as a standard of comparison, 1 and lithium andcadmium being added to one of the remaining portions, and lithium,cadmium and silver being added to the other remaining portion. Theamounts of lithium, cadmium and silver in these portions areindicated inthe table below. The ingots from each portion were poured under similarconditions and then rolled into sheet about 1 inch in thickness, Sixstandard test specimens were machined from each sheet and all were heattreated at 980 F. for minutes, quenched in cold water :and thenartificially aged 12 hours at 320 F. The tensile properties of thealloys from each portion as shown by the average results from tests madeon the specimens are listed in the following table:

Per cent Per cent Per cent Percent Tensile Yield 1 Alloy oi Ll of Cd ofAg elon ain alloy in alloy in alloy m l. None None .None 57, 000 35, 00018. 0 2 1.0 0.15 None 82.195 75,900 ,7.8 3 1.0 0.15 0.15 80,650 74.5007.5

from all three portions, the beneficial eifect of lithium-cadmium andlithium-cadmium-silver combinations on the tensile properties of heattreated and artificially aged aluminum-copper alloys is apparent.

' The claims whereinv thephrase the balance substantially all aluminum"is employed include the elements, particularly the hardening elements,which are frequently added to aluminum base alloys toimprove certainspecific properties and also the usual impurities of iron and silicon.

I claim:

1. A magnesium-free aluminum base alloy conot the testsmade onthespecimenstaining from 1 to 12 per cent copper, from 0.01

to 2 per cent lithium, from 0.01 to 1.5 per cent to 2 per cent lithium,

zinc.

0.01 to 2.0 per cent lithium,

characterized by a higher tensile and yield strength in the 'heattreated .and aged condition than the same alloy not containing bothlithium and cadmium.

2. A magnesium-tree aluminum base alloy containing from 1 to 12 per centcopper, from 0.01 from 0.01 to 0.5 per cent zinc and the balancesubstantially all aluminum, said alloy being characterized'bya highertensile and yield strength in the heat treated and aged condition thanthe same alloy not containing both lithium and zinc.

3. A magnesium-nee containing from 1 t6 12 per cent copper, from 0.01 to2 per cent lithium, from 0.02 to 1.5 per cent total of cadmium and zinc,the zinc not exceeding about 0.5 per cent, and the balance substantiallyall aluminum, said alloy being characterized by a higher tensile andyield strength in the heat treated and aged condition than the samealloy not containing lithium, cadmium and 4. A magnesium-free aluminumbase alloy containing from 3 to 0.01 to 2.0 'per cent lithium, at leastone of the elements selected from a group consisting of cadmium,mercury, silver, tin, indium and zinc, these elements being present inthe proportion of about 0.01 to 1.5 per .cent each of cadmium, mercury,silver, tin, indium, and about 0.01 to 0.5 percent of zinc, the total ofthese elements not exceeding about 1.5 per cent, and the balancesubstantially all aluminum, said alloy being characterized by a highertensile and yield strength in the heat treated and aged condition thanthe same alloy not containing both lithium and at least one of themetals from said group.

5. A magnesium-tree aluminrn base alloy containing from 3 to 5 per centcopper, from 0.01 to 2 per cent lithium, from 0.01- to 1.5 per centcadmium and the balance substantially all aluminum, said alloy beingcharacterized by a higher tensile and treated and aged condition thanthe same alloy not containing .both lithium and cadmium.

6. A magnesium-tree aluminum base alloy containing from 1 to 12 per centcopper, from at least one of the selected from a group consisting ofmercury, silver. tin, indium and zinc, these elements being present inthe proportion of about 0.01 to 1.5 per cent each of cadmium, mercury,silver, tin, indium, and about 0.01 to 0.5 per cent 01' zinc, the totalof these elements not exceeding about 1.5 per cent, and the balancesubstantially all aluminum, said alloy being tensile and yield strengthin the heat treated and aged condition than the same alloy notcontaining both lithium cadmium,

and at least one of the metals from said group.

m M. LE BARON.

aluminum base alloy 5 per cent copper, from yield strength in the heat'

